1. Field of the Invention
This invention relates to the production of alcohols by the direct hydration of the lower linear olefins, ethylene, propylene, and n-butenes. It relates particularly to the preparation of isopropyl alcohol from propylene. Still more particularly, it relates to a process for hydrating C.sub.2 -C.sub.4 olefins in the presence of a crystalline aluminosilicate zeolite catalyst having a silica to alumina ratio of at least 12, and a Constraint Index hereinbelow defined of 1 to 12, such crystalline zeolite catalyst being exemplified by HZSM-5.
2. Prior Art
The production of isopropyl alcohol by reaction of the olefin with sulfuric acid is an old and widely practiced process. Nevertheless, it has several serious disadvantages, the more important of these being the corrosiveness of the acid, the necessity of diluting the acid to recover the alcohol product, and the consequent necessity to reconcentrate the acid prior to recycling to the process. Because of these disadvantages, it has been proposed to directly hydrate olefins in the presence of various solid catalysts. Phosphoric acid deposited on silica gel or clay, as well as tungsten oxide, are typical examples of such previously proposed solid catalysts. However, while these catalysts obviate the handling problems associated with sulfuric acid, they in turn tend to introduce new complications, notably the production of comparatively large amounts of undesirable polymer and ketone. Phosphoric acid in particular also is eluted during the process and requires that makeup acid be added to the feed to maintain catalyst activity. Furthermore, such prior catalysts have generally required temperatures in excess of about 500.degree. F. to obtain reasonably satisfactory yields and selectivities. (See Brennstoff Chemie 34, 330, 1953.) The use of organic ion-exchange resins of the sulfonic acid type is described in U.S. Pat. No. 2,813,908 issued Nov. 19, 1957. Such resins are unstable above temperatures of 150.degree. C. U.S. Pat. No. 3,076,039 issued Jan. 29, 1963 describes the use of molybdenum-promoted silica-alumina catalyst to convert propylene to isopropanol. U.S. Pat. No. 3,760,024 issued Sept. 18, 1973, discloses the conversion of C.sub.2 -C.sub.4 paraffins and/or olefins to aromatic hydrocarbons with a crystalline aluminosilicate of the ZSM-5 type, at a temperature of 100.degree. to 700.degree. C.